Fluid control is important in a number of applications where one or more fluids are being mixed together. Industrial processes, such as paper production and compounding of consumer care products, rely on fluid control and circulation managements to help attain intended product attributes. Other applications, such as waste water treatment, fuel injectors, small scale power generators, and pool filtration and cleaning systems, are a few other examples where fluid control is important. Recent work in improving energy consumption in pool systems has placed greater emphasis on fluid management in pool systems.
Pool systems include a pump, a filter, a number of return lines that terminate at returns or return jets, a skimmer, and a main drain. The pump will pull water from the pool through a skimmer, or main drain. The water is passed through a filter and then filtered water is returned to the pool under pressure through a variety of returns that control flow direction and flow rate. Returns are also referred to as pool jets and are generally mounted on the pool wall below the surface. The water is returned to the pool through the pool jets to create circulation and mixing of the pool water. Under normal conditions it is expected to run a system until at least one turnover of the pool's water is achieved. Turnover is the amount of time it takes a pool system to circulate the volume of water in a given pool. The turnover time is dependent on how fast the pump is able to circulate water, typically measured in gallons per minute (gpm) and the volume of the pool water. For example, a pump that runs at 20 gpm can circulate a 12,000 gallon pool completely in 10 hours. In this example, a turnover rate in 20 hours is 2. In many cases, not all of 12,000 gallons of water will actually pass through the filter. The amount of water that is actually passed through the filter in turnover is dependent on how well the pool water itself is circulated. It is estimated that in the first turnover, only about 40% of the water actually passes through the filter. As the turnover rate increases, the percentage of water that passes through the filter drastically improves to a point, wherein further turnovers do not increase the percentage of filter water appreciably. It is believed that after 4 turnovers, the amount of water that passed through the filter is upwards of 98% of the total pool volume. Until recently, pool system efficiency was not a concern within the pool industry. There is a trend in the pool industry is toward increasing efficiency.
Pool jet returns are critical to pool water circulation and cleaning. There are three type of returns typically used in pool systems: 1) pool jets that face up toward the surface to skim the surface, 2) downward facing jets that face down for cleaning and mixing, and 3) cleaning heads that clean the lower surface of the pool and aid in cleaning and mixing. Each have pros and cons, but all three returns offer limited or poor circulation efficiency. In all cases, however, return water is forced through a nozzle that directs flow and controls flow rates based on the diameter through which the return water passes.
Upward facing return jets are better suited for pools situated in areas where there is a lot of surface debris. The upward facing jet can “push” any floating debris toward the skimmers. The less material sitting on the floor of the pool, the cleaner the pool will be, and the lower amount of chemicals are required to maintain it. Such returns, however, provide poor circulation. With the skimmer pulling water from the surface and the pool jet returning water to the surface, very little circulation occurs in the deeper parts of the pool. This creates dead zones as well as layering of the pool water. The cold water will sit near the bottom of the pool while the warmer water will sit at the surface. When a heater is being used, this can create uneven heating. Furthermore, layering can result in longer heating times to achieve desired pool temperature. With the jet return facing up, surface area is increased through creation of ripples in the pool, creating faster rates of evaporation and heat loss, resulting in more water and heater usage.
Downward facing jets are better suited for pools in an area where very little debris material enters the pool from above. A downward facing jet, or down-jet, provides a high degree of circulation. The skimmers pull water from the surface and redistribute it downwards towards the pool bottom through the return jet. Down-jets also improve heating efficiency and reduce temperature layering in the pool by mixing warmer surface water with cooler water at the bottom. Since the heated water is not at the surface, there is a reduction of heat loss caused by surface interaction and evaporation. Down-jets do not eliminate all temperature layering. The water closer to the surface, heated by the sun, will tend to create a boundary layer of warm water. A boundary layer of warm water at the surface would suggest that surface water is not circulating within the pool system as well as it could, reducing turnover efficiency.
Pop-up cleaning heads are located along the lower surface of the pool. The pop-up heads are coupled to return lines and are typically designed to all return water to flow along the lower pool surface. Pop-up heads are normally flush with the mount structure and pool surface. At certain intervals when return water is passed through the return lines, the flow of return water cause the pop-up heads to actuate, raising a nozzle just above the lower surface of the pool. Some designs may rotate so as to distribute the return flow across a wider arc along the surface the pool. Pool systems with sets of pop-up heads can help improve circulation and push debris from the pool bottom into circulation path toward the surface where the skimmer captures the debris and directs it toward the filter.